Vehicle with automatic transmissions typically employ various approaches to control engine operation during shifting to improve drive feel. Specifically, in some cases, it can be desired to control the transmission output torque during up and/or down shifts so that a constant transmission output torque is maintained during a shift.
In some automatic transmissions, there may be large deviations in the transmission output torque during the torque and inertia phases of a shift event. In one approach, variation in the transmission output torque may be controlled by calibrating the capacity and timing of the on-coming and off-going clutches and by using spark retard to decrease the engine output torque during the inertia phase. However, while spark retard allows engine output torque to be rapidly decreased, there can be a penalty in increased fuel consumption and emissions. Further spark retard can generally only decrease the engine output torque from an optimal point.
Another approach to adjusting engine torque during a shift involves using an electronically controlled throttle. However, the responsiveness of throttle modulation may be limited by the intake manifold filling dynamics lag, and the responsiveness of the ETC actuator.
Still another approach that may be used is a crankshaft mounted starter alternator, SA, to decrease and/or increase, and modulate, the transmission input torque in response to a torque modulation request from the transmission control strategy. However, such an approach requires a sufficiently fast actuator to control the transmission input torque, such as a crankshaft mounted SA. While a SA can potentially be used to modulate the transmission input torque during a shift, the maximum torque capacity of a typical starter alternator may be less than half the engine torque capacity, thus limiting such an approach. Further, the SA torque may be inversely proportional to the SA shaft speed and may also be limited by the battery state of charge.
To address these and other issues, in one example, a method for controlling powertrain operation in a vehicle, the powertrain having an engine and an automatic transmission, the engine having at least an electrically actuated cylinder valve, is provided. The method comprises changing gears from a first discreet gear ratio to a second discreet gear ratio of the transmission; and increasing engine torque during a torque phase of said gear change by changing operation of the electrically actuated cylinder valve, and decreasing engine torque during an inertia phase of said gear change.
In this way, it is possible to generate a sufficiently high bandwidth torque increase to so that improved drive feel can be obtained during a shift, such as a shift from a lower gear to a higher gear. Further, this increase may be obtained without requiring a starter alternator or other such device, and without depleting battery storage.
In another aspect, a powertrain system for a passenger vehicle traveling on the road may be provided. The system comprises an engine, the engine having at least an electrically actuated cylinder valve; an automatic transmission; a torque converter coupled between the engine and the automatic transmission; and a controller configured to change gears from a first discreet gear ratio to a second discreet gear ratio of the transmission; and increase engine torque during a torque phase of said gear change by changing operation of the electrically actuated cylinder valve, and decreasing engine torque during an inertia phase of said gear change, wherein changing operation is adjusted based on an amount of slip across the torque converter.
In this way, it is possible not only to provide improved drive feel, but improved consistency from shift to shift can be provided via the additional feedback using the slip ratio.